1. Field of the Invention
The present invention is, for example, for an image forming apparatus employing an image forming process such as electrophotographic technique or electrostatic recording technique, and relates to a method of manufacturing a tube-covered roller for use in a heat fixing device which, for a fixed image, carries out a heat fixing treatment of an unfixed toner image of image information formed and born on a recording member (including a transfer member, a print paper sheet, a light-sensitive paper sheet and an electrostatic recording paper sheet) according to a transfer mode or a direct mode in an image forming process portion.
2. Description of Related Art
As a fixing device included in an image forming apparatus employing electrophotographic technique or electrostatic recording technique, there has widely been used a so-called heating roller type heat fixing device which fixes an unfixed toner image, as a permanent image, on a recording member by causing the recording member, which bears the unfixed toner image thereon, to pass through a nip portion formed by a fixing roller (heating roller) and a pressure roller which are rotated in a state of coming into pressed contact with each other.
In addition, as a heat fixing type system which does not supply electric power to a heat fixing device, particularly, at the time of standby, to reduce the power consumption to the utmost, a film heating type heat fixing device designed to fix a toner image on a recording member through a thin film between a fixing roller and a pressure roller has been disclosed, for example, in Japanese Laid-Open Patent Application No. Sho 63-313182, Japanese Laid-Open Patent Application No. Hei 2-157878, Japanese Laid-Open Patent Application No. Hei 4-44075, Japanese Laid-Open Patent Application No. Hei 4-204980, etc.
In such a heat fixing device, in order that a toner image can be fixed on a recording member without offset, a release-characteristics layer, such as a polytetrafluoroethylene (PTFE) or a perfluoroalkoxy tetrafluoroethylene copolymerizate (PFA), which shows a high ability in release characteristics, is formed on the uppermost layers of the fixing roller, the film and the pressure roller.
The release-characteristics layer is formed into a tube-like configuration, or is formed by an electrostatic spray, a dipping coating, or the like.
In addition, for the purpose of preventing the offset occurring when the surface of a fixing roller is charged up due to the conveyance of a recording member, the release-characteristics layer is sometimes doped with a conductive material such as a carbon black.
Alternatively, for example, employed is a pressure roller of the type in which a surface of the pressure roller is coated with a mixture of a fluoro rubber and fluoro-resin (fluoroplastic), such as Daiel-Latex GLS-213 (trade name, produced by Daikin Industries Ltd).
In particular, in order to satisfy a high durability and a high release stability according to the speedup of an image forming apparatus, a pressure roller covered with a tube has been employed frequently in recent years.
FIG. 6 is an illustration of a model of an example of the aforesaid pressure roller with a layer construction. A pressure roller 40 is made to have a tube-like configuration in such a manner that a sponge elastic layer 42 formed by forming a silicone rubber or a fluoro rubber, or by foaming a silicone rubber is formed on the exterior of a core 41 and a release-characteristics layer 43 made of a PTFE, a PFA, an FEP or the like is additionally formed on the sponge elastic layer 42.
As a method of manufacturing the aforesaid pressure roller 40, there has been known a method in which a core made of a metal such as aluminum is placed upright in the interior of a cylindrical mold so that a liquid silicone rubber is injected into the gap between the core and the mold to be vulcanized for curing, or a predetermined quantity of liquid silicone rubber is first injected into a blind-end cylindrical mold and a core is inserted into the mold so that the liquid silicone rubber rises in the gap between the core and the mold to cause the gap therebetween to be filled with the liquid silicone rubber, and then vulcanized for curing, and a surface of the cured silicone rubber is covered with a tube made of a fluororesin such as a PFA, a PTFE or the like and serving as the aforesaid release-characteristics layer.
However, the following problem will arise with the above-described manufacturing method as will be described hereinbelow.
The work of covering a pressure roller released from the mold with a fluororesin-made tube is difficult, so that there is a possibility that distortion occurs on the tube formed as the surface of the pressure roller or the tube is damaged.
For this reason, a method of accomplishing the formation of the silicone rubber and the coating of the fluororesin-made tube concurrently has taken place as disclosed in Japanese Laid-Open Patent Application No. Sho 50-7097, Japanese Laid-Open Patent Application No. Sho 51-27276, Japanese Laid-Open Patent Application No. Sho 61-169863, etc.
That is, as shown in FIG. 7, molds 52a and 52b constituting upper and lower end portions are fitted in a cylindrical mold 51, and the end portion mold 52a has an opening 53 for injection of a liquid silicone rubber. In manufacturing a pressure roller, a core 41 made of aluminum or the like and a fluororesin tube 43 coated with a primer after etching of its inner surface are successively mounted in and on the end portion mold 52a, and the end portion mold 52a equipped with the core 41 and the fluororesin tube 43 is fitted in one end of the cylindrical mold 51. Following this, the end portion mold 52b is fitted in an opening portion of the other end of the cylindrical mold 51, and a liquid silicone rubber 42 is injected under a high pressure through an injection opening 53 of the end portion mold 52a into the gap between the core 41 and the fluororesin tube 43 so that the gap therebetween is filled with the liquid silicone rubber 42. This filling pressure causes the expansion of the fluororesin tube 43 for the close attachment thereof to the inner circumferential surface of the cylindrical mold 51, so that the fluororesin tube 43 is integrated with the silicone rubber material 42.
Alternatively, a porous elastic material or member (silicone sponge) obtained by foaming a silicone rubber is shaped on a core and polished or ground up to a dimension of a predetermined outer diameter, while a non-shrinkable fluororesin tube having a diameter smaller than the outer diameter of the elastic material is expanded in a pressure-reducing container and the polished roller is inserted into the expanded tube. After the completion of the insertion thereinto, the assembly is again put under a normal pressure or the atmospheric pressure, so that the fluororesin tube is closely attached to an outer surface of the sponge elastic layer.
The above-described method has been employed for the fabrication of the pressure roller included in the heat fixing device.
However, the above-described pressure roller manufacturing method creates the following problems.
That is, at the setting of the fluororesin tube in the cylindrical mold or at the handling during the manufacturing process, it is considerably difficult that the pressure roller manufacturing worker performs operations without touching the surface of the fluororesin, so that there is a possibility of damages to the tube.
In addition, since the inner surface of the cylindrical mold directly comes into contact with the surface of the pressure roller at the formation, there is a possibility that the scratches or attached matters on the inner surface of the cylindrical mold are transferred directly onto the surface of the pressure roller.
Because of the above-mentioned problems, the release ability of the surface of the fluororesin layer of the pressure roller sometimes drops. In this case, when a toner image offsets at the fixing nip portion of the heat fixing device, or when a recording member is removed from the fixing nip portion in the paper ejecting direction in a case where a paper jam occurs in the image forming apparatus in such a state that the unfixed toner is on the recording member, the toner attached onto the surface of the fixing member is once carried to the surface of the pressure roller, so that the toner tends to adhere as a contaminating toner onto the surface of the pressure roller. At this time, if the pressure roller shows sufficient release characteristics, the contaminating toner adheres onto the rear surface (the surface which comes into contact with the pressure roller) of a recording member conveyed next, and the surface of the pressure roller again returns to a clean surface where no contaminating toner exists. On the other hand, if the surface of the pressure roller has flaws or scratches as mentioned above, or if attached substances exist thereon, because of no sufficient release characteristics, the contaminating toner is not completely removable, but accumulates thereon. Accordingly, in the worst case, for example, there arises a problem in that the adhesive strength by the contaminating toner increases between the recording member and the surface of the pressure roller, so that the recording member is wound around the surface of the pressure roller.
Accordingly, it is an object of the invention to provide a tube-covered roller for fixing which does not have attached substances, scratches or the like on its surface.
Another object of the invention is to provide a method of manufacturing a tube-covered roller for fixing, comprising a step of setting a core material in a substantially central portion of a cylindrical mold and setting, outside the core material, a tube and a resin layer which is capable of coming into contact with an inner surface of the mold, a step of putting a rubber material between the core material and the tube and hardening the rubber material to produce a roller, and a step of, after detaching the roller covered with the tube and the resin layer from the mold, removing the resin layer from the roller.
A further object of the invention is to provide a method of manufacturing a tube-covered roller for fixing, comprising a step of placing a resin layer on a tube, a step of covering a roller having a rubber layer with the tube having the resin layer placed thereon, and a step of removing the resin layer from the roller covered with the tube.
A still further object of the invention is to provide a method of manufacturing a tube-covered roller for fixing, comprising a step of setting a core material in a substantially central portion of a cylindrical mold, setting a tube outside the core material and setting a cylindrical resin member outside the tube in such a way as to come into contact with an inner surface of the mold, a step of putting a rubber material between the core material and the tube and hardening the rubber material to produce a roller, and a step of detaching the roller covered with the tube from the resin member left at the mold.